1. Field of the Invention
This invention is directed to azeotropic and azeotropic-like mixtures useful for flash spinning processes and other applications.
2. Description for the Related Art
U.S. Pat. No. 3,081,519 to Blades et al. assigned to E. I. du Pont de Nemours and Company, Wilmington, Del. (hereafter DuPont) discloses a process for making flash-spun plexifilamentary film-fibril strands from a fiber-forming polymer in a liquid spin agent that is not a solvent for the polymer below the liquid""s normal boiling point. As disclosed in U.S. Pat. No. 3,227,794 to Anderson et al. (assigned to DuPont), the flash-spinning process requires a spin agent that: (1) is a non-solvent to the polymer below the spin agent""s normal boiling point; (2) forms a solution with the polymer at high pressure; (3) forms a desired two-phase dispersion with the polymer when the solution pressure is reduced slightly in a letdown chamber; and (4) flash vaporizes when released from the letdown chamber into a zone of substantially lower pressure through a spin orifice.
Spunbonded products made from polyethylene plexifilamentary film-fibril strands have been produced by flash spinning a spin fluid comprised of polyethylene in a trichlorofluoromethane spin agent. However, trichlorofluoromethane is considered to be a stratospheric ozone depletion chemical, and therefore, there is a need for alternative spin agents for use in the flash-spinning process.
Flashspun products have typically been made from polyethylene. However, it is known that other polymers have higher melting points than does polyethylene and, as such, can provide a flashspun product usable at higher temperatures when compared to product made from polyethylene. Moreover, certain solvents can not dissolve polyethylene but can dissolve other polymers; therefore motivation exists to find solvents that are particularly suited to other polymers and yet satisfy the need for non-flammability and low tendency to deplete the ozone as measured by their global warming potential (GWP). The 100 year GWP can be rated on a scale from 1 for carbon dioxide to greater than 4000 for some perfluorocarbons.
Azeotropic mixtures containing perfluroalkylethylenes have been used for cleaning and drying agents as disclosed in U.S. Pat. No. 5,302,212 to Desbiendras, et al. Azeotropic mixtures have been used as spin agents in flash spinning processes as described in U.S. Pat. No. 6,153,134 issued Nov. 20, 2000 and assigned to DuPont. Spin agents containing perfluorobutylethylene for use in flash spinning are described in related, pending International Patent Application PCT/US00/22729, also assigned to DuPont. Binary azeotropic or azeotrope-like compositions of substantially constant-boiling mixtures can be characterized, depending upon the conditions chosen, in a number of ways. For example, it is well known by those skilled in the art, that, at different pressures the composition of a given azeotrope or azeotrope-like composition will vary at least to some degree, as will the boiling point temperature. Thus, an azeotropic or azeotrope-like composition of two compounds represents a unique type of relationship but with a variable composition that depends on temperature and/or pressure. Therefore, compositional ranges, rather than fixed compositions, are often used to define azeotropes and azeotrope-like compositions.